U.S. patent number 4,986,887 [Application Number 07/331,126] was granted by the patent office on 1991-01-22 for process and apparatus for generating high density hydrogen in a matrix.
Invention is credited to Sankar Das Gupta, James K. Jacobs.
United States Patent |
4,986,887 |
Gupta , et al. |
January 22, 1991 |
Process and apparatus for generating high density hydrogen in a
matrix
Abstract
A process is described wherein hydrogen and its isotopes are
dissolved in palladium metal in high density by utilizing
electrochemical methods in an electrolytic cell. The cell has an
inert anode and a palladium containing cathode, both being immersed
in an electrolyte which contains a lithium salt dissolved in an
aprotic solvent, and a small amount of water. The dissolved
hydrogen to palladium ratio in the palladium bearing cathode, which
may be achieved by this process, is in excess of 0.95.
Inventors: |
Gupta; Sankar Das (Toronto,
Ontario, CA), Jacobs; James K. (Toronto, Ontario, M5R
3C2, CA) |
Family
ID: |
23292720 |
Appl.
No.: |
07/331,126 |
Filed: |
March 31, 1989 |
Current U.S.
Class: |
205/639; 204/292;
204/242; 376/100 |
Current CPC
Class: |
C25B
1/04 (20130101); C01B 3/0026 (20130101); G21B
1/00 (20130101); C25B 11/04 (20130101); Y02E
60/32 (20130101); Y02E 60/366 (20130101); Y02E
30/10 (20130101); Y02E 60/327 (20130101); Y02E
60/36 (20130101) |
Current International
Class: |
C25B
1/04 (20060101); C25B 1/00 (20060101); C25B
11/00 (20060101); C25B 11/04 (20060101); C01B
3/00 (20060101); G21B 1/00 (20060101); C25B
001/02 () |
Field of
Search: |
;204/129,242,292 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Dandapani et al., "Electrolytic Separation Factors on Palladium",
Journal of Electroanalytical Chemistry, vol. 39, 1972, pp. 315-332.
.
Farkas, "On the Electrolytic Separation of the Hydrogen Isotopes on
a Palladium Cathode", Trans. Faraday Soc., Apr. 1937; pp.
552-558..
|
Primary Examiner: Niebling; John F.
Assistant Examiner: Gorgos; Kathryn
Attorney, Agent or Firm: Rogers, Bereskin & Parr
Claims
We claim:
1. A process for retaining hydrogen gas, and its isotopes in a
mixed state, in high density in a palladium bearing matrix, said
hydrogen and its isotopes having been generated by electrolysis of
water, comprising the steps of:
(a) providing a palladium bearing cathode and an inert anode;
(b) providing an electrolyte comprising:
(i) a lithium salt,
(ii) an aprotic solvent having higher solubility for said lithium
salt than for lithium hydride, thereby enhancing the retention of
hydrogen and its isotopes in said palladium bearing cathode, and
containing said lithium salt in a concentration not exceeding 10
Molar, and
(iii) water in a concentration less than 0.1M;
(c) immersing said cathode and said anode in said electrolyte;
(d) connecting said cathode and said anode so immersed to an
external electrical energy source, said energy source being adapted
to provide electrical potential difference between said anode and
said cathode of magnitude of at least 200 mV in excess of the
potential difference required to electrolyze water, thereby
generating hydrogen and its isotopes as a mixture at said cathode,
and simultaneously retaining said generated hydrogen and its
isotopes in said cathode; and
(e) continuing the generation of hydrogen and its isotopes until
said palladium bearing cathode is saturated, and hydrogen and its
isotopes are evolving in gaseous form at said cathode.
2. A process according to claim 23, wherein, the electrolyte
additionally comprises a supporting electrolyte.
3. A process according to claim 2 wherein, said supporting
electrolyte is a tetraalkyl ammonium salt.
4. A process according to claim 3, wherein said tetraalkyl salt is
at least one of the group consisting of: tetrabutylammonium
tetrachloroborate and tetrabutyl ammonium perchlorate.
5. A process according to claim 1, wherein said hydrogen and its
isotopes are recovered from said palladium bearing cathode in a
separate step, subsequent to said electrochemical process.
6. A process as claimed in claim 1, wherein the electrical
potential difference between said anode and said cathode is adapted
to be gradually increased to a magnitude in excess of 3.5
volts.
7. A process according to claim 1 or 6, wherein the aprotic solvent
comprised in the electrolyte is at least one member of the group
consisting of;
hexamethyl phosphoramide, acetonitrile, tetrahydrofuran,
dimethoxyethane, sulphur dioxide, nitromethane, nitro-ethane,
dioxolane, diethyl ether, methyl-tetrahydrofuran, 3,5-dimethyl
isooxazol, 2,5-dimethyl furan, polyethylene oxide, and
polypropylene oxide.
8. A process according to claim 1 or 6, wherein the lithium salt
comprised in the electrolyte is at least one member of the groups
consisting of: lithium halide, lithium perchlorate, lithium
perborate and lithium haloborate.
9. A process according to claim 1 or 6, wherein the water comprised
in the electrolyte also contains oxides of hydrogen isotopes.
10. A process according to claim 1 or 6, wherein the water
comprised in the electrolyte is heavy water (D.sub.2 O).
11. A process according to claim 1 or 6, wherein the water
comprised in the electrolyte contains at least one of the group
consisting of: water soluble acid and water soluble base.
12. A method according to claim 1 or 6, wherein the generated
hydrogen and its isotopes retained in the palladium matrix of said
cathode has an atomic ratio of at least: Hydrogen and isotopes to
palladium 0.95.
13. A palladium bearing cathode configuration to be utilized in the
process according to claim 1 for retaining hydrogen mixed with its
isotopes in high density, said hydrogen and its isotopes having
been generated in an electrolytic process wherein said cathode is
immersed in an electrolyte containing water, a lithium salt and an
aprotic solvent, comprised of:
an electrode body having a relatively large surface area, made of a
predominantly palladium containing matrix which is capable of
dissolving hydrogen and its isotopes, and an electrically
conducting electrode lead in electrical contact with said electrode
body, said electrode lead having a relatively small surface area
compared to that of the electrode body, wherein the ratio of a
first amount of hydrogen the electrode body is capable of
dissolving to a second amount of hydrogen dissolved by the
electrode lead, is in excess of 1,000, said first amount being
related to the surface area of said electrode body exposed to the
electrolyte, and said second amount being related to the surface
area of the electrode lead exposed to the cell atmosphere above the
electrolyte.
14. A cathode configuration as recited in claim 13, wherein the
electrically conducting electrode lead is a palladium containing
wire.
15. A cathode configuration as recited in claim 13, wherein the
electrically conducting electrode lead has a negligible hydrogen
solubility.
16. A cathode configuration as recited in claim 13, wherein the
electrode body is comprised of a plurality of irregular shapes of
relatively small cross-section being in electrical contact with one
another within said body.
17. An electrolytic cell adapted to generating hydrogen and its
isotopes in the process according to claim 1 at a potential
difference of at least 200 mV in excess of the electrical potential
difference required to electrolyze water, and retaining said
generated hydrogen and its isotopes in high density in a cathode
having a palladium containing matrix comprised in said cell, and
said electrolytic cell having a gaseous cell atmosphere above an
electrolyte contained therein, comprising:
(a) a container having at least two cell-lead wires entering said
container, adapted to provide electrical contact inside the
container with an external source of electrical energy;
(b) an electrolyte contained in said container, comprising:
(i) a lithium salt,
(ii) an aprotic solvent having a higher solubility for said lithium
salt than for lithium hydride, and containing said lithium salt in
a concentration not exceeding 10M, and
(iii) water in a concentration less than 0.1M;
(c) a palladium bearing cathode immersed in said electrolyte,
comprising: an electrode body having a predominantly palladium
containing matrix and an electrode body surface, and an
electrically conducting electrode lead having two ends and a lead
surface, one end of said electrode lead being joined to said
electrode body, the surface area of said electrode lead being
substantially smaller than the surface area of said palladium
containing electrode body, wherein the ratio of a first amount of
hydrogen and its isotopes the matrix of said electrode body is
capable of dissolving, to a second amount of hydrogen and its
isotopes dissolved in said electrode lead, is in excess of 1,000,
said first amount being related to the surface area of the
electrode body immersed in the electrolyte, and said second amount
being related to the surface area of the electrode lead exposed to
the cell atmosphere above the electrolyte, and the second end of
said electrode lead being in electrical contact with one of said
cell-lead wires; and
(d) an inert anode immersed in said electrolyte, and connected to
said second of said cell-lead wires.
18. An electrolytic cell as recited in claim 17, wherein said
electrolyte is further comprising a supporting electrolyte.
19. An electrolytic cell as recited in claim 17, wherein the water
comprised in said electrolyte further comprises oxides of hydrogen
isotopes.
20. An electrolytic cell as recited in claim 17, further comprising
a third electrode which is immersed in said electrolyte, said third
electrode being a reference electrode, which has a third electrode
lead wire connection, and said reference electrode is being
connected by said third electrode lead wire to an electrical
potential measuring device.
Description
This invention relates to producing a gas by electrolysis and,
subsequently, dissolving it in an electrode matrix.
There has been a need for obtaining hydrogen gas and its isotopes
by electrolysis and dissolving the gas in a metal, so that the
hydrogen gas can be subsequently utilized for other purposes.
It is known to use palladium for dissolving hydrogen and its
isotopes. In a publication by W. Jost entitled "Diffusion in
Solids, Liquids and Gases", Academic Press, New York, 1960, it is
described that hydrogen and its isotopes may be dissolved in
palladium in atomic densities greater than 0.5, by reacting the
palladium metal with hydrogen or its isotopes at elevated
pressures.
It is also known to dissolve hydrogen obtained by electrochemical
techniques in the palladium metal lattice. In experiments described
by B. Dandapani and M. Fleischmann, in the Journal of Electronal.
Chemistry, 39, 1972, a palladium foil electrode was immersed in a
suitable electrolyte (such as 0.5M H.sub.2 SO.sub.4 or 1M KOH), and
the foil was connected in a cell to function as a cathode. The
hydrogen generated during the electrolysis was deposited and
dissolved in the palladium foil. It was observed that initially the
alpha palladium-hydrogen phase was formed followed by the
alpha-beta transformation which was found to take place when the
hydrogen-palladium ratio had reached 0.6. Subsequent to the
hydrogen having reached this density in the metal, hydrogen
evolution with gas bubble formation was observed. The typical
cathode potential that was measured against a calomel reference
electrode during the hydrogen deposition in the foil, was found to
be -0.75 volts.
It has now been found that hydrogen to palladium ratios
substantially in excess of 0.6 can be obtained in a palladium
matrix by electrolysis.
A method has now been found for obtaining in an electrochemical
cell hydrogen dissolved in high density in a palladium bearing
matrix, wherein, a water containing electrolyte comprised of a
lithium salt, an aprotic solvent which has a higher solubility for
the lithium salt than lithium hydride, an water in concentration
less than 0.1M, is electrolyzed between an inert anode and a
palladium containing cathode.
An advantageous and novel configuration has been found that the
loss of hydrogen through the electrode leads was minimized, when
the amount of hydrogen the cathode was capable of dissolving was at
least 1000 times greater than the amount of hydrogen the electrode
lead was capable of dissolving. The first of said amounts of
hydrogen is related to the cathode surface area immersed in the
electrolyte. The second of said amounts of hydrogen is related to
the electrode lead surface that is exposed to the atmosphere above
the electrolyte level contained in the cell.
It is suggested by way of an explanation, without considering that
this is the only explanation possible, that the unexpected results
of the present invention are related to lithium hydride or lithium
hydroxide formation in the proximity of the palladium cathode
during the electrolysis process. The hydrogen generated at the
cathode surface during the electrolysis first forms lithium hydride
with the lithium ions present in the electrolyte. The lithium
hydride precipitates, which is due to its low solubility in the
electrolyte, and deposits on the cathode surface. The lithium
hydride acts as an impedance in the path of further hydrogen
generated, thereby forcing the hydrogen atoms to acquire very high
energies in order to pass through the lithium hydride to the
palladium cathode. This high energy is translated into a
beta-transformation of the palladium, which is then capable of
retaining much higher densities of hydrogen then has hitherto been
observed.
The same considerations apply to obtaining high density hydrogen
isotopes in a palladium matrix such as deuterium and tritum, when
electrolyzing heavy water contained in an electrolyte of this
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a schematic diagram of an electrolytic cell utilized
in practicing the invention,
FIGS. 2, 3 and 4 represent schematic drawings of the electrode
configuration deployed in the electrochemical hydrogen generation
of the instant invention.
The preferred embodiment of the invention will now be described by
reference to the above figures.
Palladium hydrogen alloys have been used extensively for
purification of hydrogen and even for the separation of hydrogen
isotopes, since palladium metal is highly permeable to hydrogen and
its isotopes, as was discussed hereinabove. At room temperature,
palladium can be made to absorb significant quantities of hydrogen
by either direct pressurization or by electrochemical processes
such as electrolysis. The latter technique is particularly
convenient for the production of hydrogen dissolved in
palladium.
It is known to insert palladium electrode to be alloyed with
hydrogen in water to which some electrolyte has been added to
provide electrical conductivity. The palladium is rendered
electrically negative with respect to a counter electrode or anode
to complete the electrical circuit. The anode may be platium or
other oxidation resistant electrically conducting material. The
palladium and the counter electrode are connected to an electrical
energy source, and electrical current is passed through the
electrolyte whereby the water is electrolyzed to hydrogen and
oxygen. The oxygen will generate as bubbles on the anode, that is
on the positively charged electrode, and is usually allowed to
leave the cell or is collected by some manner which is of no
particular interest in the present invention. The palladium
electrode is rendered negative, and hydrogen which will be produced
at the palladium electrode will enter into the palladium alloying
with the metal. The amount of hydrogen which can be introduced into
the palladium is limited, and once the voltage applied to the
palladium has reached a specific negative value, hydrogen bubbles
will appear on the surface of the electrode signifying that no more
hydrogen can enter into the matrix of the palladium. A further
decrease to more negative values of the applied voltage will be
ineffective in increasing the capability of the palladium cathode
to dissolve or alloy with more hydrogen.
In the preferred embodiment of the invention, the conditions under
which hydrogen can be dissolved in palladium at much higher
cathodic voltages then was hitherto possible, is illustrated by
working examples. The high density of hydrogen and its isotopes in
the palladium matrix may then be utilized as a source of hydrogen
in high energy batteries or, alternatively, may be utilized in the
process of nuclear fusion.
In another embodiment of of the invention, means of restricting the
loss of hydrogen from the palladium electrode during electrolysis
is disclosed. It is required that there is an easy electrical path
for the electric charge by means of a lead wire connecting the
palladium cathode to the electrical energy source. It is, however,
necessary to restrict the amount of hydrogen that can be lost
through this electrical lead to the surrounding atmosphere. Such
restrictions become increasingly important as the hydrogen to
palladium ratio increases and an inherent tendency of the palladium
to evolve hydrogen to the atmosphere increases as well.
Examples of electrode configurations which have been found
especially suitable in practicing the present invention will be
described hereinafter.
It was found that certain electrode structures were preferable over
others in obtaining high hydrogen-to-palladium ratios in the
palladium containing, cathode using the electrolyte of this
invention.
It was noted that high hydrogen-to-palladium ratios were obtained
using electrode configurations, when the portion of the electrical
connecting lead above the electrolyte compared to the total surface
of the palladium bearing electrode immersed in the electrolyte, was
small. This relationship is expressed as a normalized aspect ratio,
which advantageously should exceed the value of 50. This ratio
translates to an approximate solubility ratio of the hydrogen
dissolved in the palladium to that in the lead wire as being in
excess of 1,000.
The schematic drawing of the electrochemical cell utilized in
practising the present invention for obtaining high density
hydrogen and isotopes dissolved in palladium is shown in FIG.
1.
In FIG. 1, a relatively impact resistant container (16) is shown,
having a lid (17) and containing electrolyte (18) to a
predetermined level, represented by level mark (19). Reference
electrode (15) is also immersed in the electrolyte (18) in the
proximity of the palladium bearing electrode (10), to facilitate
measurement of the electrical potential of the palladium bearing
electrode during the electrolytic process. A counterelectrode or
anode (14) is shown encircling the palladium bearing electrode.
Electrical lead wires (13) providing contact to the electrodes (10,
14) (13) are introduced through the lid (17). The electrical lead
wires provide connections of the cell to the electrical energy
source and potential measuring devices (not shown).
The electrical connection of the palladium metal containing
electrode by means of a thin palladium wire (12) at contact point
(11) is shown schematically in FIG. 2. Like numerals in the figures
represent like parts of the apparatus.
Another embodiment of the palladium containing electrode and its
electrical connection is illustrated in FIG. 3, where a metal which
is a good electrical conductor such as copper and its alloys, but
has a low hydrogen solubility, is shown contacting (11) and
enclosing the palladium metal bearing electrode and having a lead
wire (30).
Another embodiment of the palladium bearing electrode configuration
is shown in FIG. 4, wherein the palladium electrode (10) is
comprised of a number of smaller interconnecting pieces. An
electrical conductor (30) which does not dissolve hydrogen in
appreciable amounts, is shown to be connected (11) to the palladium
electrode design of this embodiment. The position of the electrode
with respect to the level, indicated by the level mark (19) of the
electrolyte (18) is such that all surfaces of the pieces comprising
the palladium electrode (10) are in contact with the electrolyte
(18).
EXAMPLE 1
The invention will be described utilizing the electrolytic cell
shown in FIG. 1. The palladium electrode (10) was immersed in an
electrolyte (18) which is made up of a mixture of
hexamethylphosphoramide, lithium perchlorate in a concentration of
0.01M and tetraethylammoniumchloroborate at a concentration of
0.1M. A platinum wire (14) wound around the palladium electrode
(10) but not touching it was used as the counterelectrode, and the
potential in the proximity of the palladium electrode was measured
with a Ag/Ag+ reference electrode (15). The reference electrode was
composed of 0.01M silver nitrate and 0.1M
tetraethylammoniumchloroborate, which was held in a glass container
separated by a porous glass frit and Luggin capillary. An external
potential was applied to the palladium and platinum electrodes at
the respective leads so that to maintain the electrode potential of
the palladium electrode at -3.0 volts with respect to the reference
electrode. Water was added slowly, so that the electrolysis
provided generation of oxygen bubbles at the positively charged
counterelectrode (anode) (14) and the electrolysis was maintained
for 24 hours at the preset potential. No hydrogen gas generation by
bubbles was observed during this period at the palladium containing
cathode.
At the end of the experiment, the palladium cathode was
disconnected and placed in a vacuum chamber at 350.degree. C., and
the amount of hydrogen released from the palladium was determined.
The hydrogen-to-palladium ratio in the palladium matrix was always
found to be in excess of 0.95.
The electrode configurations shown in FIG. 3 and FIG. 4,
respectively, provided equally good results.
EXAMPLE 2
This example describes an electrolytic cell utilizing a platinum
electrode as anode and a palladium rod as cathode. A reference
electrode of Ag/0.05M AgNO3 containing 0.1M tetrabutylammonium
tetra chloroborate electrolyte was also incorporated in the
electrical circuit. The reference electrode was used to monitor the
actual cathode and anode potentials during electrolysis.
The anode, the cathode and the reference electrode were immersed in
an electrolyte. The electrolyte was made up with acetonitrile
solvent used in combination with supporting electrolyte of 0.1M
tetrabutylammonium tetra fluoroborate, and lithium perchlorate in
0.01M concentration and small amounts of water or deuterium
oxide.
In this example, the platinum wire electrode was wrapped around the
palladium cathode in such a manner that no direct contact existed
between the cathode and anode, while maintaining sufficient
exposure of the anode surface to the electrolyte. The reference
electrode was separated from the electrolyte and the anode and
cathode by a porous glass frit.
The experiments in controlled potential electrolysis were carried
out with the aid of a Princeton Applied Research Potentiostat (PAR
173, 174 & 175).
It was noticed that as the potential measured by the reference
electrode vs. the cathode decreased from -0.75 to -1.25 volts,
there was no hydrogen gas evolution at the cathodes. The
electrolysis was continued for another 8 hours at increasingly
negative electropotential without the evolution of any gaseous
hydrogen. Hydrogen evolution was only observed at the cathodic
potential of being more negative then -2.4 volts.
A similar experiment conducted with heavy water, that is deuterium
oxide, produced no deuterium evolution when the cathode potential
was lowered beyond -0.75 volts. Similarly, deuterium evolution
started only when the cathodic potential of the palladium electrode
exceeded -2.4 volts.
It can be seen that the amount of hydrogen and its isotopes, which
can be driven into the palladium lattice by the present invention
exceeds the potentials obtained in electrolizing water by
conventional means in conventional electrolytes.
The atomic ratio of hydrogen and its isotopes to palladium was
subsequently measured by releasing the amount of hydrogen in the
palladium electrode in a vacuum chamber at 350.degree. C. and
determining the amount of hydrogen evolved from the palladium
matrix. The hydrogen to palladium or deuterium to palladium ratios
observed in these experiments has always exceeded 0.95 and in some
cases were even greater than 2.
EXAMPLE 3
In this example, hexamethylphosphoramide solvent was used to
provide an electrolyte containing supporting electrolyte in
concentrations of 0.1M tetrabutylammonium tetrachloroborate,
lithium perchlorate in 0.01M concentration, in addition to the
water or deuterium oxide being present in a concentration of less
than 0.01M. The anode was a platinum wire, the cathode a platinum
rod and the reference electrode and the potentiostat were similar
to those described in Example 2.
The water contained in the electrolyte was electrolyzed by
increasing the potential difference between the anode and the
cathode while measuring the cathode potential by means of the
reference electrode. It was observed that the cathode potential has
decreased to values less than -1.25 volts without any hydrogen
evolution. Experiments were continued for 8 hours without any
hydrogen being evolved at the palladium cathode. The potential was
further diminished, and when it reached -4 volts, hydrogen
evolution had started at the palladium cathode surface.
The atomic ratio of hydrogen to the palladium contained in the
cathode matrix, was determined by releasing the hydrogen in a
vacuum chamber at 350.degree. C. and measuring the amount of
hydrogen evolved.
Several experiments were conducted as described in the above
example and it was found that the hydrogen to palladium ratio has
always exceeded 0.95, and in some cases, it was greater than 2.
The experiment was repeated with heavy water containing deuterium
oxide and similar results were obtained in obtaining deuterium
gas.
It was also noticed that lithium deposited from the
solvent-electrolyte systems around -3.5 volts measured against the
reference electrode, and the lithium deposition onto the palladium
cathode created a lithium hydroxide film. It appears that this
lithium hydroxide film further lowered the hydrogen evolution and
enabled larger quantities of hydrogen to penetrate into the
palladium cathode resulting in an even larger hydrogen density in
the palladium cathode.
Experiments similar to those described in Example 1, 2 and 3 were
conducted utilizing tetrahydrofuran as the solvent in conjunction
with lithium perchlorate and small quantities of water or deuterium
oxide. Again voltages as negative as -3.6 volts were measured and
lithium deposition was found at the cathode surface. The amount of
hydrogen dissolved in the cathode was again measured by the
technique described in Examples 1, 2 and 3, and similar very high
values which were in excess of 0.95 hydrogen to palladium ratio
were observed.
Experiments were also conducted using 1,2-dimethoxyethane as
solvent together with tetrabutylammonium perchlorate as supporting
electrolyte and lithium chloride as the lithium salt together with
small quantities of water or deuterium oxide. Similar results as
those described above were noticed and hydrogen evolution was not
started until the cathode voltage became more negative than -4.0
volts, measured against the silver Ag/Ag+ reference electrode.
In some other experiments, the solvent used was a combination of
acetonitrile and sulphur dioxide in dissolving lithium perchlorate
and small quantities of water or deuterium oxide. The final
densities of hydrogen in palladium achieved in utilizing these
solvents were as high as those observed in previous
experiments.
The examples described hereinabove illustrate that extremely high
hydrogen densities can be obtained in a palladium bearing matrix by
the novel process and electrodes of the present invention.
Although the present invention has been described with reference to
the preferred embodiments, it is to be understood that
modifications and variations may be resorted to without departing
from the spirit and scope of the invention, as those skilled in the
art will readily understand. Such modifications and variations are
considered to be within the perview and scope of the invention and
the appended claims.
* * * * *